title: Electronic and ligand properties of annelated normal and abnormal (mesoionic) N-heterocyclic carbenes: a theoretical study.
abstract: The effect of annelation and carbonylation on the electronic and ligating properties of N-heterocyclic carbenes (NHCs) has been studied quantum chemically. The thermodynamic and kinetic stability of these NHCs have been assessed on the basis of their singlet-triplet and HOMO-LUMO gaps respectively. Both annelation and carbonylation have been found to decrease the stability of NHCs. Compared to nonannelated carbenes, annelated and carbonylated carbenes are found to be weaker σ donors but better π acceptors. However, the effect of carbonylation is more pronounced than annelation toward increasing the π acidity of the NHCs. The reactivity of these carbenes has been discussed in terms of nucleophilicity and electrophilicity indices. The calculated values of the relative redox potential and (31)P NMR chemical shifts of corresponding carbene-phosphinidene adducts have been found to correlate well with the π acidity of the NHCs.
authors.affiliation: Department of Chemical Sciences, Tezpur University , Napaam 784028, Assam, India.
authors.forename: Ashwini K
authors.initials: AK
authors.lastname: Phukan
authors.forename: Ankur Kanti
authors.initials: AK
authors.lastname: Guha
authors.forename: Satyajit
authors.initials: S
authors.lastname: Sarmah
authors.forename: Rian D
authors.initials: RD
authors.lastname: Dewhurst